Empresas
Empleos
  • Sobre nosotros
  • Soluciones
    • Publicación de vacantes
      Publica tu vacante y recibe candidatos calificados en 48h.
    • Evaluación de candidatos
      500+ pruebas técnicas y psicológicas, más anti-fraude.
    • Headhunting
      Búsqueda ejecutiva a la medida de principio a fin.
    • Nómina + EOR
      Dispersión de nómina y EOR en más de 15 países de LATAM.
  • Precios
  • Empleos

0

182
Vistas
Can someone explain this condition in a react task?

I have this solution for a react task and there is something I didn't understand.

// React is loaded and is available as React and ReactDOM
// imports should NOT be used
class Input extends React.PureComponent {
  render() {
    let {forwardedRef, ...otherProps} = this.props; 
    return <input {...otherProps} ref={forwardedRef} />;
  }
}

const TextInput = React.forwardRef((props, ref) => {
  return <Input {...props} forwardedRef={ref} />
});

class FocusableInput extends React.Component {
  
  ref = React.createRef()

  render() {
    return <TextInput ref={this.ref} />;
  }

  // When the focused prop is changed from false to true, 
  // and the input is not focused, it should receive focus.
  // If focused prop is true, the input should receive the focus.
  // Implement your solution below:
  componentDidUpdate(prevProps) {
    if(!prevProps.focused && this.props.focused) this.ref.current.focus();
  }
  
  componentDidMount() {
    this.props.focused && this.ref.current.focus();
  }
}

FocusableInput.defaultProps = {
  focused: false
};

const App = (props) => <FocusableInput focused={props.focused} />;

document.body.innerHTML = "<div id='root'></div>";
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

In componentDidUpdate the task is

   // When the focused prop is changed from false to true, 
  // and the input is not focused, it should receive focus.

So prevProps.focused was false and the negation !prevProps.focused makes it true.

And this.props.focused should be true so that the condition with the logical operator && (!prevProps.focused && this.props.focused) can be true.

But the task says it should not be true // and the input is not focused

Does that mean this.props.focused should be false?

The condition wouldn't be true with ( true && false) ?

Can someone explain what I'm not seeing?

about 4 years ago · Santiago Trujillo
2 Respuestas
Responde la pregunta

0

You never check if the element has focus, you only check the props.

This should probably look like this:

if(!prevProps.focused && this.props.focused && this.ref.current !== document.activeElement) this.ref.current.focus();

But checking for this seems unnecessary since focusing focused element has no performance impact.

about 4 years ago · Santiago Trujillo Denunciar

0

The "input is not focused" is not about focused prop value, but whether the element is actually focused in the DOM. If this.ref.current is not focused, then this.ref.current.focus() will give keyboard focus to this.ref.current but if this.ref.current is already focused, then this.ref.current.focus() will not change anything anyway.

about 4 years ago · Santiago Trujillo Denunciar
Responde la pregunta
Encuentra empleos remotos

¡Descubre la nueva forma de encontrar empleo!

Top de empleos
Top categorías de empleo
Empresas
Publicar vacante Precios Comercial
Legal
Términos y condiciones Política de privacidad
© 2026 PeakU Inc. All Rights Reserved.
Andres GPT
Recomiéndame algunas ofertas
Necesito ayuda